First, preheat your oven to 425°F. Place the chicken breasts on a cutting board and cover them with a piece of plastic wrap. Using a meat mallet or a rolling pin, gently flatten the thicker end of each breast until they are all a relatively even thickness. This step is crucial for ensuring the chicken cooks evenly.
Dry the chicken breasts with paper towels to help them brown nicely. Drizzle them with oil and then sprinkle the combined salt, Italian seasoning, paprika, and pepper over the top. Place the seasoned chicken in a 9x13" baking dish, making sure they aren’t overlapping.
In a medium bowl, whisk together the heavy cream, minced garlic, corn starch, salt, and pepper until smooth. Stir in the chopped sun-dried tomatoes and shredded Parmesan cheese. Pour this creamy mixture around the chicken in the baking dish.
Place the baking dish in the preheated oven and bake for 16-20 minutes. The exact time will depend on the thickness of your chicken. Use a meat thermometer to check that the internal temperature has reached 165°F at the thickest part.
Remove the dish from the oven and stir the fresh spinach into the hot sauce around the chicken. Cover the dish with aluminum foil and let it rest for about 10 minutes. This allows the juices in the chicken to redistribute, keeping it moist, and gives the spinach time to wilt perfectly.